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Re: gEDA-user: Making an odd-shaped PCB
On Sun, 4 Feb 2007 23:27:47 GMT
msokolov@xxxxxxxxxxxxxxx (Michael Sokolov) wrote:
> Hellow PCB developers and users,
>
> As my design enters the pre-layout stage, I have a number of stupid
> newbie questions about PCB.
>
> Here is my first stupid newbie question. The board that I need to make
> is not rectangular, but has an odd shape. (See my previous post about
> copying someone else's form factor.) How does one capture the odd shape
> (cutouts and shaved corners) in PCB?
>
> Let me break this question down into subquestions:
>
> 1. How are odd-shaped boards generally made? Does the PCB manufacturer
> make a rectangular board first and then cut/shave/file it down as
> necessary?
>
> 2. In the .pcb file there is a PCB() or PCB[] record specifying the
> board size. Should I set it to the size that the rectangular board
> would have had if the answer to Q1 was 'yes', or something different?
> (A little larger?)
>
> 3. In this mailing list traffic I have overheard something called the
> outline or fab layer. What exactly is it and how does it work? And
> first of all, are "outline layer" and "fab layer" two different terms
> for the same thing, or are they two different things?
>
> 4. What should the outline layer look like? Is it a set of lines and
> arcs forming a closed path that encircles the complete shape of the
> finished PCB, however odd it is, or just the cutouts? This question
> links back to question 2, and is best illustrated by an example.
>
> Suppose my finished board needs to look like this:
>
> |<---------------------- 7672 mils ----------------------->|
> A| |B
> --+-----------------------------------+----------------------+--
> ^ | | AC mains | ^
> | | | connector | | 2040
> | | | mils
> | | This line is imaginary <--| | |
> | | | V
> 6 | +----------------------+--
> 5 | |E ^ |F
> 6 | |<--|-- 2600 mils ---->|
> 0 | | |
> | |
> m | | 4
> i | | 5
> l | | 2
> s | | 0 mils
> | | |
> | | | |
> V | | V
> --+-----------------------------------+----
> C| |D
> |<----------- 5072 mils ----------->|
>
> (This is actually a simplification, the real thing is even more
> complex!)
>
> Here's what my question boils down to: should I make the "total board
> size" as reckoned by PCB 7672 x 6560 mils (7672 mils = AB distance, 6560
> = AC distance), or something larger? If I choose the exact ABxAC
> dimensions as my PCB size, that'll be the hard boundary of the "world"
> within which PCB will allow me to draw on any layer, right? In that
> case how would I draw the whole ACDEFB shape on the outline layer? Or
> can one have lines on a layer that run exactly along the edge of the
> drawable universe? Or should my outline layer depict just the DEF
> cutout (i.e., consist of just two lines: DE and EF), with all other
> edges and corners specified implicitly by the "total board size"
> setting?
>
> 5. Is the fab/outline layer identified by a special magic layer name in
> PCB? Is it "fab" or "outline" or what?
>
> OK, this is enough stupid questions for me for today. I hope that
> someone will be kind enough to answer at least some of them. :-)
>
> MS
>
In PCB (at least the CVS version, not sure about 20060822) you can define
a "magical" layer called "outline", be sure to define it in a seperate
group. On that layer just draw the entire outline of the board using the
line (and arc?) tools. It may be a good idea to mention this layer
explicitly in a readme included with your gerbers when you send it off to
you boardhouse. I tested it with eurocircuits and it works.
I don't know how boardhouses make oddly shaped PCB's, I only know they
get more expensive if they have to throw away more unused material :-).
HTH
Hans
>
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